The present invention relates to an improved flow cell for analysis of particles in a sample fluid, which is buffered by a sheath fluid. More particularly, the present invention relates to a flow distributor for distributing the sheath fluid ranging in a first direction substantially paralleled to flow direction of flow of the sample fluid to a second direction substantially perpendicular to the flow direction of the sample fluid. The present invention also relates to a method of operating such a flow cell.
Flow cells for analyzing particles flowing in a sample fluid buffered by sheath fluid are well known in the art. See, for example, U.S. Pat. No. 4,338,024 assigned to the assignee of the present application.
Typically, flow cells of the type described hereinabove and hereinafter, are used in analytical instruments to position and present a sample fluid containing particles of interest for analysis. The more accurately that the sample fluid is positioned, the better the analysis of the particles therein can be made. Typically, the sample fluid and a sheath fluid that buffers the sample fluid are made to flow together from a large entry chamber into a small cross sectional examination area or region. The transition from the inlet or entry chambers to the examination region forms a hydrodynamic lens that squeezes both the sample fluid and the sheath fluid proportionally into the smaller space. Where the particles of interest are microscopic particles, the resulting cross-sectional space occupied by the sample fluid must position the particles within the depth of field of an instrument, such as an optical system or a laser system, to obtain the best analytical information. For the best hydrodynamic focus, a large area of sheath flow must envelop the small area of sample fluid without any swirling or vortices.
Accordingly, in the present invention, a flow cell for analysis of particles in a sample fluid, which is buffered by sheath fluid, has a flow chamber with a sample inlet for receiving the sample fluid and a sheath inlet for receiving the sheath fluid. The flow cell also has an outlet for the sample fluid and the sheath fluid with the flow cell shaped to convey the sample fluid in a flow direction from the sample inlet past an examination region to examine the particles of the sample fluid to the outlet. The flow cell also comprises a flow distributor, which is positioned between the sheath inlet and the examination region for distributing the sheath fluid ranging in a first direction substantially paralleled to the flow direction to a second direction substantially perpendicular to the flow direction.
The present invention also relates to a method of flowing a sheath fluid and a sample fluid in the flow cell past an examination area for analysis. The sample fluid is flowed in a flow direction from a sample inlet past the examination area to an outlet. The sheath fluid is flowed into the flow cell. The sheath fluid is then distributed by a flow distributor in a plurality of directions ranging in a first direction, which is substantially paralleled to the flow direction to a second direction which is substantially perpendicular to the flow direction prior to the sheath fluid flowing into the examination area. The sheath fluids with the sample fluid from the examination area are then flowed to outlet.